Mesh networking is a way to route data and instructions between nodes. A node can be any device connected to a computer network. Nodes can be computers, routers, or various other networked devices. On a TCP/IP network, a node is any device with an Internet Protocol (IP) address. Mesh networking allows for continuous connections and reconfiguration around broken or blocked paths by “hopping” from node to node until the destination is reached. Mesh networks differ from other networks in that the component parts can all connect to each other via multiple hops, and they generally are not mobile devices. In a packet-switching network, a hop is the trip a data packet takes from one router or intermediate node in a network to another node in the network. On the Internet (or a network that uses TCP/IP), the number of hops a packet has taken toward its destination (called the “hop count”) is kept in the packet header.
Wireless mesh networks employ intelligent nodes typically including a wireless (e.g. radio or radio frequency (RF)) transmitter and receiver, a power source, input devices, sometimes output devices, and an intelligent controller, such as a programmable microprocessor controller with memory. In the past, wireless mesh networks (e.g. RF networks) have been developed having configurations or networks for communication that are static, dynamic or a hybrid of static and dynamic. Power for these networks has been supplied either via wires (the nodes are “plugged in”) or from batteries in each node. As the size, power, and cost of the computation and communication requirements of these devices have decreased over time, battery-powered wireless nodes have gotten smaller; yet, the computing demands on the wireless nodes have increased.
Wireless mesh network technology can be used for deploying sensors as nodes in a variety of different environments for monitoring diverse parameters such as, for example, temperature, pressure, and humidity. These types of networks can be denoted wireless sensor networks (WSN). Each sensor in a WSN is typically powered by a battery and therefore has a limited energy supply and operational capability. Because the sensors are constantly monitoring the environment and communicating with other nodes, it is important to efficiently manage the power consumed by each sensor. Further, it is important to monitor the operational status of each of the sensors.
Given that most WSN devices are battery powered, the overall network lifetime depends on the efficiency with which sensing, computing, and data transmission by the sensors can be achieved. Because the power requirements for wireless communication by the sensors are orders of magnitude higher than the other sensor operations, it is critical that operation of the radios on these devices be managed carefully. This is primarily achieved by turning the radio on only when devices need to send and/or receive data. The operational lifetime of the network, thus, depends on the ability to identify and schedule wakeup and sleep times for the radios in the wireless network nodes.
Gateway devices can be used to interconnect a WSN or an RF network with the wired Internet Protocol (IP) and wired sensor network infrastructure. Gateway devices or network controllers can manage the WSN or RF network by providing a time basis, collecting and managing network state information, managing network device joins and leaves, and sending commands to end devices.
A key aspect of a gateway device involves providing time synchronization information to other RF devices in the WSN or RF network. The RF devices use a common time basis to schedule their wakeup and schedule cycle. A failure in the gateway or network controller can cause significant problems in the entire RF device network. First, a failure in the gateway or network controller can cause the RF devices to lose their time basis and render the RF devices unable to synchronize their wakeup and sleep cycles. Secondly, without a common time synchronization basis provided by the gateway or network controller, it is difficult for wireless network devices to communicate efficiently with each other. When a wireless network device is unsynchronized with another wireless device with which it is attempting to communicate, the radio transceivers in both devices must be active for a longer period of time to achieve a level of synchronization necessary to enable communication. This causes the wireless network devices to remain on (active) for a much longer period of time, thereby consuming a higher level of the battery power in the wireless network device. Finally, a failure in the gateway or network controller can make it difficult or impossible for new nodes to join the existing network; because a join requires the new nodes to learn the time basis of the network, and to use the global time basis for receiving network state information, and for sending and receiving control and sensor data.
U.S. Pat. No. 7,180,915 describes an apparatus, and associated method, by which to synchronize nodes in a wireless mesh network, such as a fixed broadband network or a moving ad-hoc mesh network. Time stamps are added to data packets at a reference node defined pursuant to a pseudo hierarchy. The data packets are communicated by the reference node to a receiving node. The time stamp information is extracted there from, to provide an indication of a time reference value from which the time stamp information is formed. Registers are maintained at the nodes with updated values of the timing information, used in time synchronization between the nodes of the mesh network.
U.S. Pat. No. 7,272,129 describes a method and apparatus for synchronizing a node within an ad-hoc communication system. During operation, all nodes periodically broadcast a synchronization beacon for other nodes to utilize for synchronization when a coordinating access point (node) is unavailable. A particular node's synchronization beacon will have an associated “tier” number that is incremented from the tier number of the beacon used to synchronize the particular node. In the absence of an access point, a node that joins the ad-hoc communication system will listen for synchronization beacons transmitted by other nodes. If synchronization beacons are heard, the node will synchronize with a beacon having a lowest tier. The node will then broadcast its own beacon having its tier number incremented from the lowest tier beacon heard.
Thus, an apparatus and method for adapting to failures in gateway devices in mesh networks are needed.